Like how a knight gets promoted for killing the dragon, what if someone who kills all the knight becomes a more fearsome-looking dragon their next turn.
Seeing that they will cap the lobbies to 8 players, and its (15?) rounds, unless RNG favors picking them, you would only see this upgrade(s) 1-2 times in a full game, maybe 3-4 times in a smaller to minimal lobby, assuming you live that long.
This would only benefit from smaller lobbies, otherwise useless. Its much easier to upgrade as a knight since you will play most of your rounds in a game as one.
Don’t get me wrong, I like the idea, just no way of doing it the way you said.